Sound wave digitizers are known in the art as shown, for example, in U.S. Pat. No. 4,317,005 and in U.S. Pat. No. 4,012,588. In U.S. Pat. No. 4,317,005, a pair of linear or Sell-type transducers bound a pair of intersecting edges of a data surface and transmit acoustic waves to a passive reflecting target, such as a stylus. Reflected waves are detected and the timing thereof determined to locate the target by its coordinates. In FIG. 3 of U.S. Pat. No. 4,012,588, a transmitting transducer emits sound waves from an edge of a data space and reflected waves are received by a pair of receivers at the corners of the same edge of the data space and isolated from the transmitting transducer by acoustic barriers, and a triangulation computation is made to determine the location of an object in the data space.
Low cost narrow beam electrostatic transducers are well known in the art. In my U.S. application Ser. No. 496,158, filed May 19, 1983, and entitled "EFFICIENT LOW COST TRANSDUCER SYSTEM" now U.S. Pat. No. 4,530,077 I disclose a novel ultrasonic transducer using a low cost narrow beam electrostatic transducer coupled with a beam transformer or acoustic lens located in the near field thereof for controllably expanding the transmitted beam in one dimension.
The object of the present invention is to provide an improved two dimension sound wave digitizer. A further object of the invention is to provide a sound wave digitizer or data entry device using low cost transducers. Another object of the invention is to provide a compact sound wave digitizer.
In accordance with this invention, a pair of sound wave beam transducers transmit a pair of angularly related sound beams along orthogonally related paths across a data surface; the beam transducers being spaced from intersecting edges of the data surface a distance substantially equal to the maximum edge dimension of the data surface so that the sound beams impinging on an object over the data surface are substantially orthogonal. The sound beams are preferably in the ultrasonic range propogated in air.
In accordance with a preferred form of the invention, a pair of low cost narrow beam electrostatic transducers combined with conical beam transformers are spaced at a distant remote point from the edge of a data surface wherein a randomly movable object, such as a stylus or human finger or other object, may be located. The spacing of the transducer from the edge is such that the angle at any intersection point of the beams is substantially orthogonal. The beams are folded 180 degrees to achieve compactness and the form factor is enhanced by the beams being coplanar and coupled to the folding acoustic mirror by intersecting coplanar acoustic horns. Sound absorbing material is utilized to form beam boundaries in said acoustic horns.